Phase shifters delay a signal so that the phase of the signal is shifted by a desired amount, typically measured in degrees or radians. A distributed phase shifter is one in which the phase shift occurs along the entire length of the device. Controlled phase shifters are used in numerous optical and microwave applications such as modulation schemes in coherent-optical communication systems, control of microwave phased array antennas, and signal processing applications in optics and microwave systems.
Analog phase shifters typically utilize a varying DC bias level to achieve a desired phase change of a radiation signal propagating through a waveguide. The relationship between DC bias level and phase shift, however, it generally not a linear one.
Digitally controlled phase shifters typically utilize a digital to analog converter to produce an analog signal required for phase modulation. The utilization of digital to analog converters, however, increases complexity, cost, and power consumption.
It is thus an object of the invention to provide a digitally controlled distributed phase shifter that does not require the use of digital to analog converters.
It is a further object to provide a digital distributed phase shifter that linearly varies the phase of a radiation signal with changes in a digital control word applied to the phase shifter.